METHOD FOR PRODUCTION OF NdFeBCu MAGNET AND NdFeBCu MAGNET MATERIAL

ABSTRACT

A method for producing an NdFeBCu magnet includes supplying an alloy melt having a composition that is represented by the general formula Nd y Fe 100-x-y-z B z Cu X , where x is between 1 and 3 inclusive, y is larger than 12 and at most 24, and z is larger than 6 and at most 12, onto a cooled roll to obtain a quenched ribbon as a ribbon shaped magnetic material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing an NdFeBCu magnet and an NdFeBCu magnet material, and, more particularly, to a method for producing an NdFeBCu magnet that has a coercivity that is comparable or superior to that of an magnetic material that contains a rare metal such as Dy, Tb, Co or Cr without the addition of a large amount of the rare metal and an NdFeB-type magnet material for the NdFeBCu magnet.

2. Description of the Related Art

Magnetic materials are broadly classified into two groups: hard magnetic materials and soft magnetic materials. Hard magnetic materials are required to have a high coercivity, whereas soft magnetic materials are required to have a high maximum magnetization even if their coercivities are lower. The coercivity typical of hard magnetic materials is a characteristic relating to the stability of magnet, and as the coercivity is higher, the magnet can be used at a higher temperature and has a longer life.

NdFeB-type magnet is known as a magnet of a hard magnetic material. It is known that an NdFeB-type magnet can contain fine textures. It is also known that a liquid-quenched ribbon that contains fine textures can be improved in coercivity. However, the NdFeB-type liquid-quenched ribbon that contains fine textures does not have sufficient temperature characteristics as a magnetic material, and various proposals have been therefore made to improve the coercivity-temperature characteristics thereof.

For example, Japanese Patent Application Publication No. 2000-252107 (JP-A-2000-252107) describes a semi-hard magnetic material which is represented by the composition formula Fe_(100-x-y)B_(x)R_(y)M_(z) (where Fe represents iron, B represents boron, R represents at least one rare-earth element selected from the group consisting of La, Ce, Pr, Nd and Sm, and M represents at least one element selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au and Pb), and which forms an alloy melt in which x, y and z in the composition formula satisfy the relations 7 atomic %=x<15 atomic %, 0.5 atomic %=y=4 atomic %, and 0.1 atomic %=z=7 atomic %, respectively, and contains a-Fe microcrystal that has an average crystal grain size of 100 nm or smaller as a constituent phase. As a specific example, a semi-hard material that has a coercivity which is lower than 10% of an NdFeB-type magnet as a hard magnetic material is disclosed.

In addition, Domestic Re-publication of PCT International Application 2002-030595 (JP-A1-2002-030595) describes a method for producing a magnetic material alloy that includes the steps of preparing an alloy melt that has a composition that is represented by the general formula Fe_(100-x-y-z)R_(x)Q_(y)M_(z) (where R represents at least one of Pr, Nd, Dy and Tb, Q represents at least one of B and C, and M represents at least one of Co, Al, Si, Ti, V, Cr, Mn, Ni, Cu, Ga, Zr, Nb, Mo, Ag, Pt, Au and Pb, and where x, y and z satisfy the relations 1 atomic %=x<6 atomic %, 15 atomic %=y=30 atomic %, and 0 atomic %=z=7 atomic %, respectively), forming a thin strip-shaped alloy by quenching the alloy melt by a strip casting process using a cooling roll. As a specific example of quaternary-type alloy, a quenched thin strip-shaped alloy that has a composition that has an Nd content of 5.5 atomic % or less and contains Co and/or Cr is disclosed.

However, these known magnetic materials require the addition of a large amount of a rare metal such as Dy, Tb, Co or Cr to improve the coercivity-temperature characteristics.

SUMMARY OF THE INVENTION

The present invention provides an NdFeB-type magnetic material that has a coercivity that is comparable or superior to the magnet which is obtained when a rare metal such as Dy, Tb Co or Cr is added, without the addition of a large amount of the rare metal.

A first aspect of the present invention relates to an NdFeBCu magnetic material that includes a quenched ribbon composed of an Nd—Fe—B—Cu alloy.

In the NdFeBCu magnetic material according to this aspect, the Nd—Fe—B—Cu alloy may have a composition that is represented by the general formula NdFeBCu_(A), and A may be a number that represent an atomic percent and may be between 1 and 3 inclusive.

In the NdFeBCu magnetic material according to this aspect, the Nd—Fe—B—Cu alloy may have a composition that is represented by the general formula Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X), where x, y, and z may be numbers that represent atomic percents, x may be between 1 and 3 inclusive, y may be a number that is larger than 12, and z is a number that may be larger than 6.

In the NdFeBCu magnetic material according to this aspect, y may be larger than 12 and at most 24 and z may be larger than 6 and at most 12. Alternatively, y may be 14 or larger and z may be 7 or larger.

In the NdFeBCu magnetic material according to this aspect, the Nd—Fe—B—Cu alloy may have a composition that is represented by the general formula Nd₁₅Fe₇₇B₇Cu₁.

In the NdFeBCu magnetic material according to this aspect, the Nd—Fe—B—Cu alloy has a composition of a quaternary alloy composed of Nd, Fe, B and Cu.

A second aspect of the present invention relates to a method for producing an NdFeBCu magnet that includes supplying an alloy melt having a composition that is represented by the general formula Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X), where x is between 1 and 3 inclusive, y is larger than 12 and at most 24, and zis larger than 6 and at most 12, onto a cooled roll to obtain a quenched ribbon as a ribbon shaped magnetic material.

The method according to this aspect may further include: removing columnar crystalline textures from the quenched ribbon; pulverizing the quenched ribbon from which the columnar crystalline textures have been removed; and subjecting the quenched ribbon, which has been pulverized, to pressure sintering to obtain a bulk body.

In the production method according to this aspect, subjecting the quenched ribbon to pressure sintering may include subjecting the quenched ribbon to electric current heating for 5 to 100 minutes under conditions of a contact pressure during sintering of 10 to 1000 MPa, a temperature that is 550° C. or higher and 600° C. or lower, and a vacuum of 10⁻² MPa or less.

In the method according to this aspect, y may be 14 or larger, and z may be 7 or larger.

In the method according to this aspect, the alloy melt may be composed of Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X) that has been molten at a temperature of 1400 to 1700° C., and supplying an alloy melt onto a roll may include spraying the alloy melt onto the roll, which has a peripheral speed of 1.0 to 3.2 m/sec, under reduced pressure or in an inert gas atmosphere under conditions of a clearance of 0.6 to 1.2 mm and a spray pressure of 0.2 to 2 kg/cm³.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a graph that shows the coercivity-temperature characteristics of a quenched ribbon according to one embodiment of the present invention and quenched ribbons according to comparative examples;

FIG. 2 is a graph that shows the normalized coercivity-temperature characteristics of a quenched ribbon according to one embodiment of the present invention and quenched ribbons according to comparative examples; and

FIG. 3 is a schematic view of a single-roll furnace for use in the production of a quenched ribbon in examples of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present inventors conducted earnest studies to accomplish the above object and have reached the conclusion that an NdFeB-type magnet composed of multi-domain particles does not develop a coercivity without a magnetic field phase that prevents displacement and generation of domain walls and the coercivity-temperature characteristics thereof cannot be improved with the three elements alone. Then, as a result of additional studies, the present inventors have accomplished the present invention.

Description is hereinafter made of an embodiment of the present invention with reference to the drawings. Referring now to FIG. 1 and FIG. 2, the quenched NdFeBCu_(i) according to the embodiment of the present invention is generally comparable or superior in coercivity-temperature characteristics to a quenched NdFeBCo₁₀ ribbon. It is believed that the high-temperature coercivity of the quenched NdFeBCu₁ ribbon indicates the fact that a magnetic material that has excellent coercivity-temperature characteristics can be obtained since fine textures are formed when a quenched ribbon is produced from the alloy melt that has the above composition. Here, a quenched ribbon is a thin strip or a ribbon that can be obtained by quenching an alloy melt.

The magnetic material of this embodiment needs to be a quenched .ribbon (a ribbon-shaped magnet material) composed of an Nd—Fe—B—Cu. It is believed that isolated fine textures that are smaller than the single-domain particle diameter or isotopic fine textures are formed in the quenched ribbon and a high coercivity based on a coherent rotation model can be achieved.

The Nd—Fe—B—Cu_(A) in this embodiment is a quaternary alloy that is composed of Nd (Neodymium), Fe (Iron), B (Boron) and Cu (Copper) and is obtained by substituting Cu for a part of one of the elements, such as B, of a ternary alloy which is composed of Nd, Fe and B. The Nd—Fe—B—Cu alloy in this embodiment may have a composition that is represented by the general formula NdFeBCu_(A), and A may be a number that represent an atomic percent and may be between 1 and 3 inclusive. There are some elements that are effective to improve the room-temperature coercivity when added to the above alloy but no element except Cu has been found that is effective to improve the temperature characteristics.

In this embodiment in particular, a quenched ribbon that has good coercivity-temperature characteristics can be obtained by creating an NdFeB-type quenched ribbon that has a composition that is richer in Nd or B than that of the stoichiometric region (Nd₁₂Fe₈₂B₆). Thus, the Nd—Fe—B—Cu preferably has a composition that is represented by the general formula Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X) (where x, y and z are numbers that represent atomic percents and are in the ranges 1=x=3, 12<y and 6<z, respectively), more preferably Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X) (1=x=3, 12<y=24, particularly 14=y=24, and 6<z=12), and most preferably Nd₁₅Fe₇₇B₇Cu₁.

One method to obtain the quenched ribbon is quenching by, for example, a melt spinning process. One specific means for accomplishing this is to produce a quenched ribbon using a roll. One specific example is a method that includes supplying an alloy melt having a composition that is represented by the general formula Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X) as described above onto a cooling roll under reduced pressure or in an inert gas atmosphere under conditions of a roll peripheral speed of 1.0 to 3.2 m/sec, a clearance of 0.6 to 1.2 mm, a spray pressure of 0.2 to 2 kg/cm³, and a melt temperature of 1400 to 1700° C., quenching the alloy melt on a surface of the roll to convert the alloy into fine textures, and peeling the ribbon-shaped magnetic material off the cooling roll.

The quenched Nd—Fe—B—Cu alloy ribbon of this embodiment can be obtained by preparing an alloy ingot from specified amounts of Nd, Fe, FeB and Cu that give the above atomic percents in a melting furnace, such as an arc melting furnace, and casting the resulting alloy ingot with a casting device, such as a roll furnace that includes, for example, a melt reservoir that reserves alloy melt, a nozzle that supplies the melt, a cooling roll, a winder, a motor for the cooling roll, a winder motor, and a cooler for the cooling roll.

A bulk body can be obtained from the quenched Nd—Fe—B—Cu_(A) ribbon of this embodiment by, for example, a method that includes pulverizing the quenched ribbon or the residual that remains after the removal of columnar crystalline textures from the quenched ribbon, and subjecting the pulverized material to electric current sintering with an electric current sintering apparatus including dies, a temperature sensor, a control unit, a power supply unit, a heating element, electrodes, a heat insulating material, a metal support, and a vacuum chamber.

The pressure sintering can be carried out by means of electric current sintering for 5 to 100 minutes under conditions of, for example, a contact pressure during sintering of 10 to 1000 MPa, a temperature between 550° C. and 600° C. inclusive, and a vacuum of 10⁻² MPa or less.

Examples of the present invention are described below. In each of the following examples, the magnetic characteristics of the quenched ribbon were measured with a VSM measurement system (vibrating sample magnetometer system) manufactured by Lake Shore Cryotronics, Inc. In each of the following examples, the quenched ribbon was formed using a single-roll furnace that is schematically shown in FIG. 3.

Example 1 is described below. Specified amounts of Nd, Fe, FeB and Cu that gave an atomic ratio of Nd, Fe, B and Cu of 15:77:7:1 were weighed and an alloy ingot was prepared in an arc melting furnace. Then, the alloy ingot was melted by applying high-frequency waves in the single-roll furnace. The alloy melt was then sprayed onto a copper roll under the following single-roll furnace use conditions, thereby obtaining a quenched ribbon. Single-roll furnace use conditions were nozzle diameter: 0.6 mm, clearance: 1.0 mm, spray pressure: 0.4 kg/cm³, roll peripheral speed: 2.5 m/sec, and melt temperature: 1450° C. The magnetic characteristics of the resulting quenched Nd₁₅Fe₇₇B₇Cu₁ ribbon were evaluated using the high-temperature VSM. The result is summarized in FIG. 1 and FIG. 2. In FIG. 2, the normalized coercivity means the magnetic force of the quenched ribbon normalized with respect to its room-temperature coercivity taken as 1.

Comparative Example 1 is described below. Specified amounts of Nd, Fe, FeB and Co that gave an atomic ratio of Nd, Fe, Co and B of 15:67:10:8 were weighed and an alloy ingot was prepared in an arc melting furnace. Then, a quenched ribbon was formed in the same manner as in Example 1. The magnetic characteristics of the resulting quenched Nd₁₅Fe₆₇CO₁₀B₈ ribbon were evaluated using the high-temperature VSM. The result is summarized in FIG. 1 and FIG. 2.

Comparative Example 2 is described below. Specified amounts of Nd, Fe, and FeB that gave an atomic ratio of Nd, Fe and B of 15:77:8 were weighed and an alloy ingot was prepared in an arc melting furnace. Then, a quenched ribbon was formed in the same manner as in Example 1. The magnetic characteristics of the resulting quenched Nd₁₅Fe₇₇B₈ ribbon were evaluated using the high-temperature VSM. The result is summarized in FIG. 1 and FIG. 2.

The room-temperature coercivities of the quenched ribbons obtained as results of the evaluation using the VSM are summarized below: quenched Nd₁₅Fe₇₇B₇Cu₁ ribbon coercivity (kOe)=19.8; quenched Nd₁₅Fe₇₇B₈ ribbon coercivity (kOe)=18.6; and quenched Nd₁₅Fe₆₇Co₁₀B₇ ribbon coercivity (kOe)=19.8.

The above results also indicate that the ternary-type quenched Nd₁₅Fe₇₇B₈ ribbon has a low room-temperature coercivity but a magnetic material that has a high room-temperature coercivity can be obtained when a part of B is substituted by Cu to form a quaternary-type quenched Nd₁₅Fe₇₇B₇Cu₁ ribbon. In addition, when a part of B is substituted by Cu to form a quaternary-type quenched Nd₁₅Fe₇₇B₇Cu₁ ribbon, a magnetic material that has excellent coercivity-temperature characteristics can be obtained without adding a large amount of a rare metal such as Dy, Tb, Co or Cr.

According to the present invention, a magnetic material that is has a high high-temperatre coercivity can be obtained with reduced costs and resource risks and an inexpensive NdFeBCu magnet that has a high coercivity can be provided.

While some embodiments of the invention have been illustrated above, it is to be understood that the invention is not limited to details of the illustrated embodiments, but may be embodied with various changes, modifications or improvements, which may occur to those skilled in the art, without departing from the scope of the invention. 

1-12. (canceled)
 13. A method for producing an NdFeBCu magnet comprising: supplying an alloy melt having a composition that is represented by the general formula Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X), wherein x is between 1 and 3 inclusive, y is larger than 12 and at most 24, and z is larger than 6 and at most 12, onto a cooled roll; quenching the alloy melt on a surface of the roll to convert the alloy melt into fine textures; peeling the alloy melt that has been quenched off the roll to obtain a quenched ribbon as a ribbon-shaped magnetic material; removing columnar crystalline textures from the quenched ribbon; pulverizing the quenched ribbon from which the columnar crystalline textures have been removed; and subjecting the quenched ribbon, which has been pulverized, to pressure sintering to obtain a bulk body, wherein subjecting the quenched ribbon to pressure sintering is carried out by subjecting the quenched ribbon to electric current heating.
 14. The method according to claim 13, wherein subjecting the quenched ribbon to pressure sintering includes subjecting the quenched ribbon to electric current heating for 5 to 100 minutes under conditions of a contact pressure during sintering of 10 to 1000 MPa, a temperature that is 550° C. or higher and 600° C. or lower, and a vacuum of 10⁻² MPa or less.
 15. The method according to claim 13, wherein y is 14 or larger, and z is 7 or larger.
 16. The method according to claim 13, wherein the alloy melt is composed of Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X) that has been molten at a temperature of 1400 to 1700° C., and supplying an alloy melt onto a roll includes spraying the alloy melt onto the roll, which has a peripheral speed of 1.0 to 3.2 m/sec, under reduced pressure or in an inert gas atmosphere under conditions of a clearance of 0.6 to 1.2 mm and a spray pressure of 0.2 to 2 kg/cm³.
 17. The NdFeBCu magnetic material manufactured by using the method according to claim 13, the NdFeBCu magnetic material comprising a quenched ribbon composed of an Nd—Fe—B—Cu alloy.
 18. The NdFeBCu magnetic material according to claim 17, wherein the Nd—Fe—B—Cu alloy has a composition that is represented by the general formula NdFeBCu_(A), and A is a number that represents an atomic percent and is between 1 and 3 inclusive.
 19. The NdFeBCu magnetic material according to claim 17, wherein the Nd—Fe—B—Cu alloy has a composition that is represented by the general formula Nd_(y)Fe_(100-x-y-z)B_(z)Cu_(X), x, y, and z are numbers that represent atomic percents, x is between 1 and 3 inclusive, y is a number that is larger than 12, and z is a number that is larger than
 6. 20. The NdFeBCu magnetic material according to claim 19, wherein y is 24 or smaller, and z is 12 or smaller.
 21. The NdFeBCu magnetic material according to claim 19, wherein y is 14 or larger, and z is 7 or larger.
 22. The NdFeBCu magnetic material according to claim 19, wherein the Nd—Fe—B—Cu alloy has a composition that is represented by the general formula Nd₁₅Fe₇₇B₇Cu₁.
 23. The NdFeBCu magnetic material according to claim 17, wherein the Nd—Fe—B—Cu alloy has a composition of a quaternary alloy composed of Nd, Fe, B and Cu. 